Activities of the principal brain vesicular monamine transporter, VMAT2, are key to understanding the cellular compartmentalization of monoamines that may play a key role in modulating the actions and neurotoxicities induced by amphetamine and related psychostimulants. In previous FYs, investigators in this Branch identified cDNAs encoding human VMAT2. In this FY, they completed work cloning murine VMAT2 cDNA and genomic DNA clones from ES cell lines and defining VMAT2 genomic structure and transcriptional initiation sites. Sequence analysis of 5' flanking sequences revealed a putative promoter region containing several consensus sequences for transcription factor binding. Analyses of these cDNA and genomic clones has allowed construction of targeting vectors for deletion of several VMAT2 exons in homologous recombinant "knockout" mice. Homozygous knockouts die shortly after birth, but heterozygous mice display differences in responses to amphetamine reward and locomotion that point strongly toward differential impact of amphetamine-induced vesicular release on these two processes. They also display altered sensitivity to MPP+ dopaminergic toxicity. These mice substantially enhance our understanding of mechanisms of psychostimulant and dopaminergic neurotoxin action.